Catalysts for preparing aromatics from synthesis gas

ABSTRACT

Aromatic hydrocarbons useful as fuels are formed by passing a mixture of CO and hydrogen (synthesis gas) over a mixture of a copper-chromium promoted iron catalyst and a type Y mole sieve at elevated temperatures and pressures.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Division of Application Ser. No. 890,331 filed Mar. 27, 1978,now U.S. Pat. No. 4,139,550, which in turn is a continuation-in-part ofApplication Ser. No. 722,292, filed Sept. 10, 1976, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a process for the conversion of CO andhydrogen to aromatic hydrocarbon mixtures which are useful as fuels inautomobile engines and the like. More particularly, this inventionrelates to a one-step conversion of CO and hydrogen to said aromatics inthe presence of a novel catalyst composition comprising a mixture of apromoted iron catalyst defined hereinbelow and a mole sieve also definedbelow.

Belgian Pat. No. 828,228 (together with corresponding British Pat. No.1,495,794 and French Pat. No. 2,268,771) describes a process for theconversion of synthesis gas to a liquid product containing a highproportion of C₅ ⁺ olefins, isoparaffins and/or aromatics, using aCO-reduction catalyst in combination with a crystalline aluminosilicate(zeolite). This patent, however, requires that said zeolite have (1) anSiO₂ /Al₂ O₃ ratio of greater than 12; and, as defined by said patent,(2) a "constraint index" of 1 to 12; and (3) a "crystal frameworkdensity" of not less than 1.6 grams/cc.

By contrast, the present invention employs as the zeolite component a Yzeolite having an SiO₂ /Al₂ O₃ ratio of no greater than 6. Moreover, asthe Belgian patent itself teaches, Y zeolites do not fall within itsdefined ranges of the constraint index and crustal framework density.

U.S. Pat. No. 3,972,958 and Storch et al, Fischer-Tropsch and RelatedSynthesis, John Wiley, New York, 1951, pp. 428-434 also bear on thesubject of this invention.

SUMMARY OF THE INVENTION

In accordance with the present invention, it has now been found thatsynthetic fuels having a high aromatic content may be prepared in onestep from synthesis gas, i.e., a mixture of CO and H₂, by contactingsaid gas with a novel catalyst composition comprising a mixture of acopper-chromium promoted iron catalyst and an aluminosilicate, both ofwhich components are defined hereinbelow.

DESCRIPTION OF THE INVENTION

The process of this invention may readily be carried out by simplypassing the synthesis gas over the catalyst mixture, preferably inpelleted form, in a conventional manner, e.g., in a fixed bed reactor.The synthesis gas should comprise an essentially pure mixture of CO andH₂, and especially should be free of H₂ S, which would poison thecatalysts of this invention.

The CO--H₂ mixture used herein is a well-known mixture of gasesobtainable by conventional methods from methane, methanol, coal, or thelike. The mole ratio of CO to H₂ should desirably be in the range offrom about 1.5:1 to 1:1.5, and preferably should be about 1:1.

The rate at which the gas is passed over the catalyst, i.e., the gashourly space velocity, is in the range of 1000 to 10,000, and preferablyis 2000 to 4000. The temperature should be in the range of 300° to 350°C., preferably about 325° C., while the pressure is desirably 100-1500psig, preferably about 500-750 psig.

The catalyst, as described above, comprises a physical mixture of acopper-chromium promoted iron catalyst and an aluminosilicate, i.e., atype Y mole sieve, both of which components are commercially availablematerials. This mixture desirably contains the two components in ratiosof 0.1 to 10.0 by volume of the promoted iron catalyst to mole sieve,preferably about 1.0. The mixture is desirably used in pelleted form,as, for example, by using 20% by weight of an acid-washed inorganicoxide binder such as alumina.

The copper-chromium promoted iron catalyst component should desirablycomprise about 1 to 20 wt. % copper; 1 to 20 wt.% chromium, and theremainder iron, i.e., from 60 to 98 wt.% iron. One example of this typeof catalyst is a commercial preparation known as Girdler "G-8" (GirdlerCatalysts, Louisville, Ky., a division of Chemtron Corporation), whichcontains 90 wt.% iron, 7 wt.% copper (as the oxide) and 3 wt.% chromium(as the oxide).

Alternatively, a like promoted iron catalyst component may be routinelyprepared using a simple mixture of copper chromite and iron, preferablybut not essentially in a 1:1 to 1:2 volume mixture.

In some cases it is desirable, but not essential, to promote the ironfurther with less than about 2% alkali or alkaline earth oxides in orderto maximize the yield of liquids as opposed to gaseous products.

The aluminosilicate is a commercially available material, i.e., an HYmole sieve (conventionally obtained by heating an ammonium-exchanged Ymole sieve, e.g., at 450°-500° C., to drive off water and ammonia) whichcontains less than 0.2 wt.%, of sodium cations, generally about 0.12%,an NH₄ O content of less than 4 wt.%, generally about 3.9%, (LindeCatalyst Base 33-200; Union Carbide Corp.), and has an SiO₂ /Al₂ O₃ratio of less than about 6, preferably about 5.9. After pelletizing withan alumina binder, the SiO₂ /Al₂ O₃ ratio may decrease, for example, toabout 3.3.

The product of this novel process is a liquid mixture having a boilingrange of about 38° to 350° C., and typically contains about 25-50% byweight aromatics and a low concentration of carbonyl compounds,generally not more than about 10%, which mixture is useful as anautomotive fuel.

EXAMPLE 1

The invention will now be illustrated by the following examples in whicha series of cuts of synthesis gas was contacted with the iron-mole sievecatalyst of the invention at varying GHSV's, temperatures, pressures,and the like.

The various parameters and results are shown in Table I below. It shouldbe noted that in a similar run using the iron catalyst alone without themole sieve produced a mixture showing high carbonyl and low aromaticcontent, while a run using the mole sieve along under the givenconditions gave no product at all.

In the following runs a pelleted mixture of 14-20 mesh catalystcomprising 5 cc Girdler "G-8" copper-chromium promoted iron catalyst and5 cc Linde "33-411" (i.e., 33-200 base catalyst plus binder) ultrastablehydrogen Y catalyst was charged into a fixed-bed reactor. A mixture ofCO-H₂ was fed down over the catalyst at 75 psig. The product wascondensed in an ice water condenser and the gases passed through a dryice trap and wet test meter. The conditions and results are set forth inTable 1.

                                      TABLE I                                     __________________________________________________________________________    LIQUID PRODUCTS FROM CO/H.sub.2                                                                                       BOILING RANGE                         Hourly                 Wt. %                                                                             % By FIA*       °F.                         Cut Catalyst                                                                            T° C.                                                                      GHSV                                                                              H.sub.2 /CO                                                                        Yield                                                                             Ar. Olef.                                                                             Sat.                                                                              5%  50% 95%                            __________________________________________________________________________    1   G-8 + HY                                                                            300 1100                                                                              1.3  5.7 40          150 275 371                            2         300 1100                                                                              1.3  8.6 33          137 265 443                            3         300 1100                                                                              1.1  12.4                                                                              33.0                                                                              32.6                                                                              34.4                                                                              108 283 572                            4         300 2200                                                                              1.1  8.9 40.7                                                                              39.0                                                                              20.3                                                                              109 259 510                            5         300 2200                                                                              1.1  7.1 25          155 236 576                            6         325 2200                                                                              1.1  5.3 47.2                                                                              27.9                                                                              22.9                                                                              196 366 615                            7         325 2200                                                                              1.1  7.1 24          114 258 525                            8         325 3300                                                                              1.1  2.4 50          146 302 582                            9   G-8   300 1100                                                                              1.1  10.3                                                                              17.4                                                                              19.6                                                                              63.0                                                                              167 308 560                            10        325 1100                                                                              1.1  8.3             157 298 544                            11        300 2200                                                                              1.1  18.6                                                                              15.7                                                                              62.8                                                                              21.5                                                                              108 283 572                            12        300 2200                                                                              1.1  8.6 14.6                                                                              72.6                                                                              12.8                                                                              197 321 544                            13  HY    325  200                                                                              1.3  0                                                      __________________________________________________________________________     *Fluorescent Indicator Analysis                                          

EXAMPLE 2

Iron (ferric) and copper (cupric) in the ratio of 100:10 as nitrateswere dissolved in water and a 5% excess of sodium carbonate was added toprecipitate out the metal hydroxides. This solid was washed fairly wellwith water (but not until nitrate free) and 0.5 part K₂ CO₃ added withenough water to make a paste. Following this the precipitate was driedin the oven, charged to the reactor and reduced in hydrogen at 450°-475°C. to yield a Fisher-Tropsch catalyst comprising 100 Fe:10 Cu:0.5K₂ CO₃.

This material was then mixed in a 1:1 ratio by volume with an HY molesieve containing about 0.12 wt.% of sodium cations, an NH₄ O content ofabout 3.9 wt.%, (Linde Catalyst Base 33-200; Union Carbide Corp.), andhaving an SiO₂ /Al₂ O₃ ratio of about 5.9, as defined above.

A similar catalyst was prepared by adding 100 parts of acopper-and-chromium promoted iron catalyst (Girdler "G-8"-GirdlerCatalysts), as defined above, to 2 parts of K₂ CO₃ in water to make apaste and heating the same until dry to yield a catalyst comprising100G-8:2K₂ CO₃. This material was then mixed with the HY mole sieve in a1:1 ratio by volume.

The CO and H₂ were then passed over the resulting catalysts under theconditions set forth below in Table II, and the liquid products analyzedwith the following results:

                                      TABLE II                                    __________________________________________________________________________    LIQUID PRODUCTS FROM CO/H.sub.2                                                                                              I.R. Absorbance                                                    Boiling Range      Clefin                               PRESS.           Yield,  °F.  C═C Vinyli-            RUN CATALYST  (psig)                                                                             T° C.                                                                      GHSV                                                                              H.sub.2 /CO                                                                       % C 5%  50% 95% C═O                                                                           AR  Trans                                                                             dene               __________________________________________________________________________    A   [G-8 + 2% K.sub.2 CO.sub.3 ]                                                            750  325 1100                                                                              1.1 15.4                                                                               92 301 554 None                                                                              .242                                                                              Low Low                    + HY                                                                      B             750  300 2200                                                                              1.1 21.5                                                                               92 226 419 Low .123                                                                              High                                                                              .423               1   100FE:10 Cu:                                                                            500  300 1100                                                                              1.1 24.3                                                                              135 338 633 N.A.                                                                              N.A.                                                                              N.A.                                                                              N.A                    0.5 K.sub.2 CO.sub.3                                                          + HY                                                                      2             350  300 1100                                                                              1.1 10.2                                                                              196 430 809 Very                                                                              Low High                                                                              High                                                              High                           3             500  300 1100                                                                              1.1 16.6                                                                              171 558 811 Very                                                                              "   "   "                                                                 High                           4             500  325 1100                                                                              1.1 27.2                                                                              116 348 771 Very                                                                              "   "   "                                                                 High                           5             500  325 2200                                                                              1.1 25.4                                                                              146 363 766 Very                                                                              "   "   "                                                                 High                           __________________________________________________________________________     N.A. = No Aromatics                                                      

Based on the above results, in Runs 1 to 5, it will be seen that thecombination of a Fisher-Tropsch catalyst, as taught by Storch, whenmixed with an HY zeolite, and contacted with CO and H₂ yields, at most,insignificant traces of aromatic products as compared with the yieldsprovided by the novel catalyst claimed herein, and as compared with alike copper-chromium-containing catalyst shown in Runs A and B above.

EXAMPLE 3

A series of seven runs, similar to those of Example 1, was carried outusing varying combinations of catalyst components. As will be seen belowin Table III, Run A employed no chromium, Runs B and C employed nocopper, while Run D employed neither copper nor chromium. From thesefour runs the high carbonyl content of the resulting product confirmthat both copper and chromium are needed for aromatization. That is tosay, it has been found from studies made in the course of the inventionthat aromatization is always accompanied by low carbonyl content so thatthe key analysis of the liquid products is the infra red analysis forcarbonyls.

The findings that both copper and chromium are needed for aromatizationis confirmed in Run E, where the presence of both of these componentswith the zeolite-iron mixture yields aromatics.

In Run F, containing 50-50 volume ratio of iron and copper chromite, thecarbonyl content of the product was relatively low, even without thezeolite. This product was analyzed further, as was the liquid from Run Gwhich was made with all four components, i.e., copper, chromium, ironand zeolite.

In Table IV the products from Runs F and G were analyzed by fluorescentindicator analysis to give an "aromatics" fraction. Since carbonylswould also come out in this fraction, it was further analyzed by massspectrometry to find the true aromatic content. This turned out to be 3%when no zeolite was used, compared with 19% in the four componentsystem.

                                      TABLE III                                   __________________________________________________________________________    Dependence of Aromatization on Catalyst Composition                           Catalysts reduced at 450° C. for 1 hour at 1 atmos.                    H.sub.2, then 1/2 hour at 475° C. and 68 atoms H.sub.2. -Charge        1:1 H.sub.2 :CO at 50 atmos.                                                                              CO    % Liquid                                                                           Carbonyls                              Run                                                                              Catalyst (Volume Ratio)*                                                                     GHSV °C.                                                                         Conversion                                                                          Yield                                                                              (by I.R.)                              __________________________________________________________________________    A  Iron(40), YZ(40), Copper(20)                                                                 1200 300  60    27   High                                   B  Iron + 5% Cr.sub.2 O.sub.3 (50), YZ(50)                                                      1200 290  81    56   High                                   C  Iron(40), YZ(40), Chromia(20)                                                                1200 290  83    57   High                                   D  Iron(50), YZ(50)                                                                             1200 290  74    47   High                                   E  Iron(40), YZ(40), CuCr(20)                                                                   1800 296  95    67   Low                                    F  Iron(50, CuCr(50)                                                                            1200 300-325                                                                            80    40   Low                                    G  Iron(40), YZ(40), CuCr(20)                                                                   1200 300-325                                                                            84    31   None                                   __________________________________________________________________________     *Iron = ICI 35-4, (Imperial Chemical Industries) iron catalyst;               YZ = 33-411, Linde Y zeolite;                                                 Copper = T317, Girdler copper catalyst;                                       Chromia = CrO 101, Harshaw chromiaalumina;                                    CuCr = G13, Girdler copper chromite.                                     

                                      TABLE IV                                    __________________________________________________________________________    ANALYSES OF LIQUID PRODUCTS                                                    Fluorescent                                                                             Indicator                                                                           Analysis                                                                             M.S.* % Aromatics                                                                        Actual %                                   Run                                                                              % "Aromatics"                                                                         % Olefin                                                                            % Saturates                                                                          in FIA "Aromatics"                                                                       Aromatics                                  __________________________________________________________________________    F  23      20    57     13          3                                         G  33      49    18     56         19                                         __________________________________________________________________________     *M.S. = mass spectrometer                                                

The invention claimed is:
 1. A catalyst composition useful forconverting CO and hydrogen to aromatic fuel mixtures comprising acopper-chromium promoted iron catalyst in admixture with type Ymolecular sieve having a sodium cation content of less than about 0.2wt.%, an SiO₂ /Al₂ O₃ weight ratio of less than about 6.0, and an NH₄ Ocontent of less than about 4 wt.%, wherein the volume ratio of ironcatalyst to molecular sieve is about 0.1 to 10.0.
 2. The composition ofclaim 1 wherein the volume ratio of iron catalyst to mole sieve is 1.0.3. The composition of claim 1 wherein the catalyst mixture is inpelleted form in combination with an inorganic oxide binder.
 4. Thecomposition according to claim 1 wherein the promoted iron catalystcomponent comprises 1 to 20 wt.% copper, 1 to 20 wt.% chromium, and 2 to98 wt.% iron.
 5. The composition according to claim 1 wherein thepromoted iron catalyst component is a 1:1 to 1:2 volume ratio mixture ofcopper chromite and iron.